This invention relates generally to liquid crystal display devices and more particularly to liquid crystal display devices including means for preventing the activation of liquid crystal material under the leads connecting to the elctrodes and for accommodating misalignment of the front and rear substrates.
Liquid crystal devices include a liquid crystal material sandwiched between two substrates. The inner surface of each of the substrates is provided with a patterned conductive coating. When an electric field is applied between the coatings, those portions of the liquid crystal material which lie between those portions of the conductive coatings between which there is applied an electric field change characteristics as by becoming light scatterers or changing their plane of polarization. Where both conductive coatings are transparent, the display is backlighted and the cell selectively transmits light. If the coating on the back side is reflective, ambient light is reflected from the back surface of the display to form the display.
Numerical indicators have been fabricated by employing both scattering and polarizing liquid crystal material. The complete range of numbers 0 through 9 may be displayed by employing a seven segment pattern on the front substrate. Liquid crystal display devices are extensively used in horological, calculator and other instruments.
Generally, the transparent segments are individually connected to sources of potential by transparent leads. This presents a problem since whenever the leads overlap with the conductive coating on the rear electrode, the liquid crystal material between the lead and back electrode is activated and the overlapping portion of the lead is displayed along with the associated segment.
This problem can be overcome by making the pattern on the rear electrode exactly the same configuration and size as the periphery of the front segments. Then, if the substrates are properly aligned, there is no overlap of the leads with the rear substrate conductive pattern. This requires precise alignment during manufacture, making the processing expensive.
Other solutions have been to mask the front electrodes with an opaque conductive coating. However, this gives rise to fringing at the edges of the segments because of the voltage existing between the coating and the underlying rear electrode segments.